lexer: produce correct token for single !

src/lexer/lexer.rs

@@ -187,7 +187,7 @@ impl Lexer {
             }
             [b'!', ..] => {
                 self.next();
-                TokenKind::BangEquals
+                TokenKind::Bang
             }
             [b'&', b'&', ..] => {
                 self.skip(2);

src/lexer/token.rs

@@ -210,6 +210,7 @@ impl Default for Token {
 impl Display for TokenKind {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         let s = match self {
+            Self::BangEquals => "!=",
             Self::From => "from",
             Self::Print => "print",
             Self::BitwiseNot => "~",

src/parser/mod.rs

@@ -2203,12 +2203,7 @@ impl Parser {
                 prefix(&op, rhs)
             }
             TokenKind::Dollar => self.dynamic_variable()?,
-            _ => todo!(
-                "expr lhs: {:?}, line {} col {}",
-                self.current.kind,
-                self.current.span.0,
-                self.current.span.1
-            ),
+            _ => return Err(ParseError::UnexpectedToken(self.current.kind.to_string(), self.current.span)),
         };
 
         if self.current.kind == TokenKind::SemiColon {